This application claims priority to an application entitled xe2x80x9cDevice For Controlling Power in Power Amplifier of Portable Wireless Terminalsxe2x80x9d filed in the Korean Industrial Property Office on Dec. 31, 1999 and assigned Serial No. 68286/1999, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a device for controlling voltage in power amplifier of portable wireless terminals, and more particularly to a device for controlling voltage in power amplifiers of portable wireless terminals which prevents unnecessary power consumption by effectively controlling voltage to a power amplifier included in portable communication equipment.
2. Description of the Related Art
In general, portable wireless terminals include a power amplifier for adjusting a transmission power level of a reverse link radio signal according to a receiving strength. However, such a power amplifier consumes a significant portion of the power consumed in the portable wireless terminal. Newer portable wireless terminals require the consumption of less power. One method of reducing power consumption is by controlling voltage of the power amplifiers to improve power efficiency. A device is therefore needed to control the power amplifiers with improved power efficiency allowing the power amplifiers to generate necessary power needed to transmit the maximum radio signal level. Moreover, terminals used in current CDMA type wireless terminal systems require good linearity. But, since such terminals place an emphasis on linearity, many problems arise which reduce power efficiency. Accordingly, to resolve this problem, typical CDMA type portable wireless terminals adjust bias current for controlling voltage of the power amplifiers within a range satisfying an adjacent channel interference ratio according to a sending power level so that power efficiency can be improved.
FIG. 1 is a block diagram illustrating a device for controlling voltage in a power amplifier 100 of a portable wireless terminal as stated above according to the prior art.
Referring to FIG. 1, the power amplifier 100 generally includes a two-stage amplifier. In the case where a modulation scheme requiring linearity in a system is adopted, for example, for a PSK modulation scheme, a first stage includes a Class A type amplifier 101, and a second stage includes a Class AB type amplifier 103. However, the power amplifier 100 may also include a third stage. In such a case, the power amplifier 100 includes an additional Class AB type amplifier.
In the meantime, a supply voltage of the above power amplifier is typically classified into a reference voltage Vref and a driving voltage Vcc. The reference voltage Vref is generally used as a bias supply voltage for the initial stage amplifier 101 of Class A type, and the driving voltage Vcc is used as a bias supply voltage for the end stage amplifier 103 of Class AB type. In some cases, the reference voltage Vref may be used as a base bias, and the driving voltage Vcc may be used as a collector bias.
As stated above, the initial stage of the power amplifier uses the Class A type amplifier 101 for ensuring linearity and the end stage thereof uses the Class AB type amplifier 103 for reducing power consumption. When an input signal is very small, in the Class A type initial stage amplifier 101, a problem arises since a fixed current supplied to the power amplifier is still consumed. Here, although there is a minute difference in the consumed current between real products to which the corresponding power amplifier is applied, the amount of the consumed current is typically about 100 mA. For this reason, conventionally, Vbb1 and Vbb2 are connected to the reference voltage Vref through a switch 109 to selectively reduce the consumed current.
FIG. 2 is a graph illustrating a power supplying state according to the operation of a device for selectively controlling voltage in a typical power amplifier 100 as stated above according to the prior art.
Now, the power supplying operation of the power amplifier 100 will be described in detail hereinafter with reference to FIG. 2.
Referring to the graphical representation of FIG. 2, an abscissa axis is scaled in terms of an output, and an ordinate axis is scaled in terms of a reference voltage Vref. As can be seen from the graphical representation, when the output level is increased beyond Pout2, Vbb2 is supplied as a reference voltage Vref of the power amplifier 100. On the other hand, when the output is decreased to less than Pout1, Vbb1 is supplied as the reference voltage Vref of the power amplifier 100. That is, a method of supplying power according to the prior art may be seen from the above graph. The reason for setting output levels according to whether voltage is increasing or voltage is decreasing is to prevent the power amplifier from being in an unstable state when voltage is increasing or decreasing at the same output. Such a method of supplying power according to the prior art is applied in consideration of the stability of the power amplifier.
Consequently, there is preferably a difference in power levels by above 5 dB between the Pout1 and the Pout2 for stable operation of the power amplifier.
However, in view of the above description, it can be appreciated that the level of the reference voltage is set high unnecessarily at an output between Pout1 and Pout2 at which the level of the reference voltage may be low. To date, a method of preventing a loss of power has not been implemented in the prior art.
There is therefore a need in the art for a device for and a method of controlling voltage in a power amplifier of a portable wireless terminal which prevents unnecessary power consumption by the power amplifier by effectively controlling voltage to the power amplifier.
Therefore, an object of the present invention is to provide a device for controlling voltage in a power amplifier of a portable wireless terminal which prevents unnecessary power consumption of the power amplifier by effectively controlling voltage to the power amplifier.
It is another object of the present invention to provide a device for controlling voltage in a power amplifier of a portable wireless terminal which minimizes unnecessary power consumption by the power amplifier by effectively controlling voltage to the power amplifier so that the operating time of both a portable wireless terminal using a battery and telecommunication equipment equivalent to the portable wireless terminal can be extended.
To achieve the above objects, a device for controlling voltage in a power amplifier of a portable wireless terminal according to the present invention, includes a power amplifier adapted to adjust an amplification degree of a signal inputted in response to a supply state of a reference voltage to output the adjusted signal. The device also includes a comparator/limiter adapted to compare a value of a transmitting automatic gain controlled (TX_AGC) supply voltage and a value of an operating supply voltage to output the compared result and a power supply conversion section adapted to convert a state of the compared result outputted from the comparator/limiter into a reference voltage state for application to the power amplifier as a reference voltage thereof.